Method of making bifocal lenses.



No. 869,938. PATENTED NOV. 5, 1907.

J. R.SGHWINZBR.

METHOD OF MAKING BIPOOAL LENSES.

APPLICATION FILED 00131. 1906.

nnrrsn sra'rns PATENT orrron Joann. sonwiuznng on roan, N. AssIoNen TOTHE .usvnowrrz Mi iNosAoTuRI-No I company, A cone-cannon on NEW JERSEY.

mason OF MAKING nInoeAL menses.

PatentedNov. 5, 1907.

To all whom 'it may concern:

Be it known that I, JOHN R. Scuwmznn, a subject I of the Emperor ofGermany, residing at the-city of New York, in the borough of Manhattanand State of New York, have invented certain'new and useful Improvementsin Methods of Making Bifocal Lenses, of which the following is a lull,clear, and exact description.

My invention relates to a method of making bi-focal lenses, andparticularly lenses of this character in which the line of junctionbetween the component lenses or sections is invisible.

The object of the invention is to provide a method which shall besimpleand efficient for producing lenses of this character. I

A further object of the invention is to secure a lens having the abovecharacteristics which shall have perfoot optical properties for each ofits component parts. and in which the line of junction is absolutelyinvisible.

With these and other objects in view, my invention consists in theorder, character, and sequence of operations hereinafter more fully setforth, as illustrated in the drawing, and finally particularly pointedout in the appended claims= My invention further consists'in theconstruction, combination, location and arrangement of parts of thecompleted article, as also more fully hereinaiter set forth, andparticularly pointed out in the appended claims.

In' the drawings, Figure 1 is a view in cross section showing a bi-iocallens embodying the principles of,

my invention in the first stage of its construction; Fig. 2 illustratesdiagrammatically one of the initial steps of my' process; Fig. 3illustrates a later stage of the process; Fig. 4 shows oneof the finalsteps of the process embodying the principles of, my invention; and Fig.5 is a perspective view showing the completed article.

It will be understood that for persons obliged to use glasses, noparticular lens can be made which is in itself suitable to allrequirements. The person is continually looking first at far and then atnear objects, and with a single lens, the best that can be done is tomake a compromise between the two extremes which are really required.Lenses have been manufactured in which the far and near focus componentparts were placed side by side having a line of division extendinghorizontally across the center of the spectacle frames. This isobjectionable since the line of separation .is always apparent and isconiusing. It is accordingly very desirable to produce a glass whichshall have the two focal lengths, for .iar and near objects, in whichthe component parts shall so merge together that the line of separationis not visible. A method which has been proposed makes use of twoseparate glass lenses whi h are fused together at their adjoining faces,so that after fiu sion the two are welded into an integral singlestructgr the lenses become soft at the temperature of fusion and arequite liable to warp out of their proper shape, there by destroying thecorrect optical properties of the glass. The process is one requiring agreat deal of skill and is very expensive.

In carrying out my present invention I grind what I shall term the mainor major lens into its correct form, and I afterwards fuse the auxiliaryor secondary lens thereto. Instead of employing [or my auxiliary orsecondary lens a material which has substantially the same fusiontemperature as the major lens, I make .the secondary or auxiliary lensof a material which has a considerably lower fusion point than the majorlens, so

, that the-two may becpmewelded tOgGthelMjlbhOlll; warping or destroyingthe optical properties of-the main lens.

Referring now to the drawings and to the various views and referencesigns appearing thereon in which like parts are designated by the samereference sign, 1 indicates a main or major lens which may be ground toconvex or concave or plane-convex or concave ,form, andto any desiredlength of focus, and upon one oi the faces or surfaces thereof, Iinitially grind or other; wise form a second or auxiliary lens surface2. In Fig. 1 of the drawing I have illustrated the main or major lensportion 1 as a lano-convex lens having the auxiliary lens surface 2ground'upon' a portion of its plane surface. The grinding and polishingof the different surfaces is accomplished in the usual and well knownway which need not be particularly described in this specification.

Having obtained a main or major lens portion with the secondary surface2 ground therein, I place a pellet 3 of .material more easily fusiblethan the glass of the major lens, into the cavity formed by the surface2. Many different sorts of material may be used for the pellet 3, and Ido .notdesire to be limited or restricted to any particular material orcomposition, but I have found that very superior practical results areobtained by employing the composition known as stress which may beconveniently obtained upon the market for the manufacture of thewell-known paste diamonds. This material may be composed so that it hasan index of refraction widely different from the usual hint and crownglass used in optical work, and, by proper se- The disadvantage of thisprocess is that lection of the basic materials may be brought to afusion point considerably below that of the glasses mentioned.

An approximate composition of stress composition is as follows: pureflint or rock crystal heated white and cooled in water, pulverized anddried, three parts cream of tartar and 1*} parts of white lead. Thiswhen melted with calcined borax and saltpeter produces the stresscomposition known to commerce. When, therefore, a

blow pipe flame 4 (Fig. 2) or any other suitable method "lens 1 whileheated sufficiently for a perfect welding union, is not heatedsufficiently to become warped or change its optical characteristics orproperties in any Way. At the same time since the pellet composition iscompletely melted, it is free to acquire a homogeneous characterthroughout its mass. and insures against any air bubbles remainingbetween the adjoining surfaces.

The final step of my process comprises grinding the surface of thepellet 3, and for thispurpose I make use of a grinding wheel 5, or anyother suitable grinding or abrading means so as to impart a uniformsurface to the pellet which may be made uniform with that of the majorlens 1. Under these circumstances the exterior form of the completebi-focal lens is exactly the same as allens having the characteristicsof its main or major portion, but owing to the different index ofrefraction of the material fused on to the surface 2, the lens has adifferent focal length, and in other respects different opticalproperties, at the poltion occupied by thefused pellet. I

The respective focal lengths of the major and auxiliary lenses aregoverned by the curvatures ,of the exterior surfaces and the surface 2.The focal length of the auxiliary lens is also dependent on theparticular fusible compound used. I take advantage of this latter factas a means of accurately adjusting the focal lengths. By varying thesubstances or compositions used, as, for example, by varying thequantity of white lead added to the stress composition, the index ofrefraction and focal length of the auxiliary lens may be minutelydetermined to satisfy any particular requirements without altering majorlens surfaces.

In Fig. 5 I have illustrated a complete bi-focal lens having the main ormajor portion 1 of the usual elliptical form adapted for eye-glasses,and a small circular section 6 formed by material fused to the main lensand having a different index of refraction therefrom,

the curvatures of the l l l l l I l in the manner above described. Toordinary appearances the complete glass is a simple lens of ordinaryform, and it is only by close inspection, or by analyzing its opticalproperties, that its bi-focal character is made to appear.

While I have particularly described a method of carrying out my invention, and a particular form of the article produced thereby, I do notdesire to be strictly limited to the details shown and described. Forexample, it is not essential to make use of a pellet of the aforesaidsubstance melted by a blow pipe as above described, it being equallywithin the province of my invention to melt the fusible compound in acrucible or in any other way, and pour it upon the surface of the majorlens in a molten state.

What I claim, iszl l. The method of making a bi-focal lens whichconsists in grinding and polishing a piece of glass to form a-lens witha secondary or auxiliary lens surface upon a portion thereof, fusing andwelding a'material more fusible than glass to such secondary orauxiliary surface, said material being in any natural state or conditionof form, without being around or fitted to the surface of the lens, andfinally polishing the surface of the material so added.

2. The method of making a bifocal lens which consists in grinding andpolishing glass to form a main or major lens having an auxiliary orsecondary lens surface thereon,

fusing stress of a composition more easily melted than glass to suchauxiliary surface, said strass being in any natural state or conditionof form without being ground or fitted to the surface ofthe lens andfinally grinding an polishing; the same.

3. The method of making a bi-Iocal lens having a major portion and aminor or auxiliary lens portion of any de-,

and finally fusing the material to an auxiliary lens surface -95 5. Themethod of making a bi-focal lens which consists I upon the face of anydesired main or major lens.

in forming a ground and polished lens with an auxiliary surface thereon,of a comparatively refractory matei1al,

and fusing-and welding 11 more fusible material to suchauxiliarysurface.

In witness whereof, I subscribe .my signa tu'i'ei'jin he presence of twowitnesses.

Witnesses 2 'CARL Jussnn,

KATHARINE llIcCAnRAN.

JOHN R. scnwmznaln f

